1. Field of the Invention
The invention relates to a method for the adaptive filtering of signals as well as an arrangement for the adaptive filtering of signals.
2. Background of the Art
A known method for performing adaptive filtering consists of using an output signal of a filter, used especially as a reference, as a reference signal for comparison with an output signal of a filter carrying out the adaptive filtering, and adjusting the parameters of the adaptive filter on the basis of the comparison results.
With known adaptive filters different approaches are followed. For example, some adaptive filters provide a compromise, one between a requirement at a fixed adaptation speed to adapt as quickly as possible, if only the echo is present, and a requirement not to regulate the adaptive filter during cross-talk, with this occurring more frequently the greater the adaptation speed.
There is a problem particularly during the use of adaptive filters with so-called echo cancellers, which are used primarily in telecommunications and in particular during voice transmission—the so-called Voice over IP (VoIP)—that the reference signal is superimposed on greatly varying interference signals. In this field of application one speaks of so-called double-talk (cross-talk), the simultaneous speaking of two remote participants in the communication. Here the reference signal represents the superimposition of local signals, the so-called near-end signals of the local participant, and the echo from it on the part of the remote participant.
An optimal adaptation behavior therefore requires that the speed of the adaptation be adapted to the relationship of reference signal to the interference signal, with the level of the reference signal usually needing to be determined.
For example, a method known from EP 1 320 941 B1 consists of estimating an amplification factor between a residual echo occurring on the transmission channel, used as the reference signal, and a remote, so-called far-end signal and determining the level of the residual echo from it. Other methods again rely on an estimate of the residual echo based on the correlation between the near-end signals and the far-end signals.
From U.S. Pat. No. 6,226,380 B1 is known a method and arrangement of distinguishing between echo path change and double talk conditions in an echo canceller.